US President Donald Trump left China on Friday with no major breakthroughs on trade or tangible help from Beijing to end his Iran war, despite two days spent heaping praise on his host, Xi Jinping.

Trump's visit to America's main strategic and economic rival, the first by a US president since his last trip in 2017, had aimed for tangible results to beef up his sagging approval ratings ahead of crucial midterm elections.

The summit was filled with pageantry, from goose-stepping soldiers to tours of a secret garden, but behind closed doors Xi issued a stark warning to Trump that any mishandling of China's top concern Taiwan could spiral into conflict.